My outboard's ECU re-boots at random times when running at higher RPM's (usually) and when engine in at operating temp. More detail: The single computer tone sounds just like the key were turned on for the initial computer test... If the engine is running at speed (3-5K RPM) this happens so...
Running along and the engine suddenly (for 1/2 second) losses all power, alarm on engine control panel chirps once (similar to sound when starting engine), after the 1/2 second the engine power is restored. Another interesting thing, the GPS shuts down when this happens but other less sensitive...
